Hydrofluoroolefins (HFOs), such as tetrafluoropropenes (including 2,3,3,3-tetrafluoroprop-1-ene (HFO-1234yf)), are now known to be effective refrigerants, fire extinguishants, heat transfer media, propellants, foaming agents, blowing agents, gaseous dielectrics, sterilant carriers, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents, displacement drying agents and power cycle working fluids. Unlike chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), both of which potentially damage the Earth's ozone layer, HFOs do not contain chlorine and, thus, pose no threat to the ozone layer. In addition, HFO-1234yf is a low global warming compound with low toxicity and hence can meet increasingly stringent requirements for refrigerants in mobile air conditioning.
Two known precursors used to prepare HFO-1234yf include 1,1,1,2-tetrafluo-2-chlororopropane  (HCFC-244bb) and 1,1,1,2,2-pentafluoropropane (HFC-245cb). Indeed, numerous gas phase reactions are known for the production of HFO-1234yf by HCFC-244bb dehydrochlorination, and HFC-245cb dehydrofluorination, respectively. U.S. Pub. No. US2007/0197842, for example, teaches the synthesis of HFO-1234yf through gas phase HCFC-244bb dehydrochlorination in the presence of a carbon- and/or metal-based catalyst (e.g. nickel or palladium based catalysts). U.S. Pub. No. US2009/0043136 teaches the preparation of HFO-1234yf through gas phase HCFC-244bb dehydrochlorination in the presence of a catalyst selected from the group consisting of (i) one or more metal halides, (ii) one or more halogenated metal oxides, (iii) one or more zero-valent metals/metal alloys, or (iv) a combination of two or more of the foregoing. U.S. Pub. No. US2007/0100175 teaches the production of HFO-1234yf through gas phase HFC-245cb dehydrofluorination in the presence of a catalyst selected from the following: aluminum fluoride; fluorided alumina; metals on aluminum fluoride; metals on fluorided alumina; oxides, fluorides, and oxyfluorides of magnesium, zinc and mixtures of magnesium and zinc and/or aluminum; lanthanum oxide and fluorided lanthanum oxide; chromium oxides, fluorided chromium oxides, and cubic chromium trifluoride; carbon, acid-washed carbon, activated carbon, three dimensional matrix carbonaceous materials; and metal compounds supported on carbon. Applicants, however, have recognized that these gas phase dehydrohalogenation reactions are operated at a high temperature, typically above 400° C., to obtain meaningful yield. Because higher temperature can increase costs associated with production, there is a need in the art for a new and convenient low temperature process of preparing HFO-1234yf from HCFC-244bb and/or HFC-245cb.
While not specifically relating to the production of HFO-1234yf, U.S. Pat. No. 6,548,719 does disclose a low temperature process for producing fluoroolefins by dehydrohalogenating a halofluorocarbon with an alkali metal hydroxide in the presence of a phase transfer catalyst. The reaction is conducted at a temperature range of −5° C. to 40° C. with an optimal temperature being about 25° C. While numerous starting reagents are exemplified for the production of HFO-1234ze, HFO-1225zc, and CF3CBr=CF2, U.S. Pat. No. 6,548,719 does not expressly provide, however, a method for manufacturing HFO-1234yf, let alone a dehydrohalogenation method using HCFC-244bb and/or HFC-245cb as starting reagents. Furthermore, the exemplified reaction temperature (−5° C. to 40° C.) is too low to achieve meaningful activity with 244bb/245cb dehydrohalogenation because the halogen to be eliminated in 244bb/245cb is attached to the middle carbon, which is more difficult to be removed. Accordingly, there is a continuing need for a new low temperature process for preparing HFO-1234yf from HCFC-244bb and/or HFC-245cb.
The present invention and the embodiments presented herein address at least this need.